1. Field of the Invention
The present invention relates to the construction of an active matrix display device such as an active matrix liquid crystal display (LCD) device.
2. Description of the Related Art
In an active matrix LCD device, thin-film transistors are arranged on a sheet of quartz or glass at a high density. It is increasingly required in recent years to raise the level of integration of the thin-film transistors. On the other hand, it is more and more required for the LCD device to provide larger display areas to meet the growing demand for large-screen displays. This is where the LCD device greatly differs from large-scale integrated (LSI) circuits which are required to provide higher integration levels and smaller physical sizes.
Besides the requirement for large-screen display, it is desired to make the conductor lines of the LCD device as narrow as possible so as to provide an increased aperture ratio. If, however, narrow conductor lines are used, problems arising from their increased resistances will become evident.
The active matrix LCD device requires means for masking the thin-film transistors arranged in individual pixels as well as masking means, which is known as a black matrix, for masking edges of individual pixel electrodes. Generally, these masking means including the black matrix are separately arranged from the conductor lines. Such a construction is not preferable though because it complicates processing steps needed for the production of the active matrix LCD device.
One method for reducing conductor line resistance is to use aluminum as a wiring material. However, the use of aluminum could give rise to reliability problems because electrical contacts between aluminum and semiconductor and between aluminum and a transparent conductive coating, which is usually a thin layer of conductive oxide such as indium tin oxide (ITO), are liable to become unstable.